Powders consisting of very small particles are commonly used in the inhalation therapy where the size of the particles are of utmost importance. The diameter of particles which are to be inhaled must be less than 10 .mu.m, preferably between 6 to 1 .mu.m, to ensure adequate penetration of the particles into the bronchial area of the lungs.
Most finely divided powdered medicaments, such as micronized powders, are light, dusty and fluffy and they often create problems during handling, processing and storing. For particles having a diameter less than 10 .mu.m the van der Waals forces are generally greater than the force of gravity and consequently the material is cohesive and tends to form irregular agglomerates. Powders having such particle sizes are also very sensitive to electrostatic charges which readily arise in such powders during handling. These powders have very poor free-flowing properties and during handling bridges between the particles will be formed leading to the build up of the aggregates.
When finely divided powders are to be filled into reservoirs, compartments, cavities or depressions of different kind and sizes, such as cavities provided on an elongate carrier, for example a layer of foil, a piece of moulded plastic or similar, the aggregates must be broken down in order to make possible the filling of the powder into the cavities. One way of avoiding the build up of aggregates and to break down those that have been formed is to subject the finely divided powder to movement, e.g. agitation. This could be done by using mechanical devices, such as stirring means, or by using electronical means such as means creating ultra sound or similar.
This break-down of aggregates is especially important when small amounts, e.g. between 10 mg to 0.1 mg, in particular 5 mg to 0.5 mg, of finely divided powdered medicaments are to be filled into cavities formed to receive the required exact amount of the powder.
Another important factor when filling medicaments is the degree of compaction. This is especially important when filling finely divided medicaments into cavities which, in particular, are to be used for inhalation with breath-actuated, dry-powder inhalators, as the medicament must be lifted out of the cavities by the force created by the airstream produced by the patient during inhalation.
The powder present in the cavities must also be able to break down into the particles having a particle size smaller than 10 .mu.m during inhalation in order to provide a dose comprising high proportion of particles within the respiratory range of less than 10 .mu.m. The compaction may therefore not be too strong. On the other hand, in order to avoid the possibility that the medicament falls out of the cavity when it is positioned for inhalation but before it has been inhaled, the medicament must be compacted to a certain degree so that it is retained in the cavity until inhalation. A controlled compaction is therefore of utmost importance.